Safety limit-stop.



L. c. HART. SAFETY LIMIT STOP.

v APPLICATION FILED JAR.1C,1-918- 1 1,113,337, Patented 0ct,13,1914.

WITNESSES: INVENTOR. M

ATTORNEY.

ll NITED STATES PATENT OFFICE.

LESTER C. HART, OF YOUNGSTOVN, CHIC), ASSIGNOR TO 0. R. JONES, OF YOUNGSTOWN. GI-I10.

SAFETY LIMIT-STOP.

Specification of Letters Patent.

Patented Oct. 13, 1914.

To aZZ whom it may concern Be it known that I, LESTER C. HART, a citizen of the United States, residing at Youngstown, in the county of .Mahoning and State of Ohio, have invented new and useful Improvements in Safety Limit-St0ps, of which the following is a specification.

My invention relates to the control of electric motors, and particularly to the control of motors driving a machine or mechanism which has a repeated cycle of operations or travels through limited distances.

My invention can be used for thecontrol of an elevator motor, or a motor driving a hoisting mechanism on an electric crane wherein it is desired to provide a safety limit stop to stop the motor when the elevator car or hoisting device has reached a certain limit of travel. Motors driving hoisting mechanism are usually provided with suitable controllers for starting, stopping and reversing the motor, at the direction of the operator.

One of the objects of my invention is to provide a safety device which will automatically stop the motor and driving mechanism when the mechanism has reached a certain limit of travel regardless of the position or condition. of the operators controller. The device can also be used as an emergency device to stop the motor at any time if the operators controller fails to work.

Another object to provide means for reversing the motor from the operators controller after it has been stopped by the safety device, in order to restore the motor to the normal control of the operators controller and put the safety device into position for another operation. This is brought about preferably by the operator moving his controller to the usual position for reversing the motor.

7 Other objects will be obvious from the "following description and claims.

"In working out my invention, I provide a switching device, preferably operated mechanically by movement of the hoisting mechanism when it has reached a certain limit of its travel, which cuts the motor oil from the source of supply through the operators controller and connects the motor so that it acts as a separately excited generator, the armature being shunted by a low resistance which causes the motortocome 55 quickly to rest. The usual hoisting-motor 1s also through a circuit which is independent of the operators controller, so that it makes no difference whether the operator moves his controller or not, when the limit of travel is reached the safety device makes the proper connections for-stopping the motor quickly and without undue current values in the motor winding.

7 Referring to the accompanying drawing, Figure l is a diagrammatic view illustrating the principles of my invention, and Fig. 2 is a fragmentary view showing the application of my invention to a hoisting mechanism.

On the drawing, A represents the armature of an electric motor, and F, the field winding thereof.

C is a rheostatic and reversing controller having brushes 0" and 0 arranged to engage the contacts 0 c 0 and 0 in the manner presently to be described.

R and R are resistances having sections thereof connected to the corresponding sec tions of the contacts 0 and c in a wellknown and clearly illustrated manner.

0 is the controller handle by which the brushes are made to move into engagement with the contacts.

E represents a switching mechanism of the drum controller type showing in development the fixed fingers 6', e e e, c and the movable contacts g, g g g g corresponding, respectively, to the fingers, the contacts being connected together.

B is a brake-winding in the wire 1 which connects one terminal of the field winding F to the central section of the contact 0 the remaining terminal of the field-winding being connected to the negative supply wire 2. One terminal of the armature A is connected by the wire 3 to the contact c and the other, by the wire 4 to the finger 6 The positive supply wire 5 is connected to the central section of the contact 0 the branch wire 6 connecting the supply wire to the finger e The wire 7 connects the contact 0 and the finger e. The wire 8 is in series with the resistance R and connects the finger, e to the point 7) on the wire 1 between the/field winding F and the brake-winding B. The wire 9 is in series with the resistance R and connects thefinger c with the wire 3.

The contacts 9 to are supposed to be rotated by the shaft 8, to which-the pulley s is secured. The cable (Z runs over the pulley and has the weight N'suspended on one end thereof, and the heavier weight w suspended on the other end.

H is a hoisting-drum rotated by any suit able power, as the armature A, and carrying the hoisting-cable h, which passes around th sheave h in the hoisting-block k provi ed with the hoisting-hook 7L3 and the arm h which stands vertically below the weight 10 so that when the block 71 reaches a certain height, the arm will engage and lift the weight 'w thereby enabling the weight wto rotate the shaft 8 in one direction. When the arm h next descends, the weight 2'0 causes the shaft 8 to rotate in the opposite direction.

To hoist a load supported by the hook h 1 the handle 0 is moved to the right, causing the brush 0 to connect the first, section of the contact 0 and the contact 0", and the brush a to connect thefirst section of the contact 0 and the contact 05. The current fiows'froin the positive wire 5 through the contact 0 the brush 0', the contact 0*, the wire 3, the armature A, the wire 4:, the finger 6*, the contacts 9 and g, the finger e, the wire 7, the contact 0, the brush 0 the contact 0. the wire 1 and the brake-coil B, and the field-winding F to the negative sup- .ply wire 2. The current described flows in series through the half of the resistances R and R the brake-coil B, the armature A, and the field winding F, thus causing the. brake-coil to release the brake, and the motor to hoist the load at its slowest speed. The hoisting speed may be increased by moving the handle 0 step by step to the right, thereby gradually cutting out the resistances R and R until the upper member-of the brush 0 engages the central section of the contact .0 and the lower member of the brush 0 engages the central portion of the contact 0 when the motor will hoist the load at its greatest speed; When'the arm h engages the weight Q02 and lifts the same until the weight w rotates the controller drum E from theposition shown in Fig. 1 to a posi:

tion at which the contact 9 passes beyond the finger e, and the fingers e 6 c engage the respective cont-acts g g 9 In this position of the controller E, the circuit of the brake-winding B is broken at the finger e, thereby causing the brake to set in a wellknown manner. At the same time, the posi tive terminal of the field-winding F is connected to the positive supply wire 5 by means ofthe wire 6, the finger e the contacts g and 9 the finger c and the wire 8 which has the resistance R in series therewith, the field-Winding being thereby connected across the supply wires 2v and 5 and in series with the resistance R, this circuit being independent of the operators controller C. Also, the armature. A is connected in a dynamic braking circuit, as fol lows: from one terminahof the armature A through the wire 3, the resistance R and the wire 9, the finger 6 the contacts 9 and 9 the finger 6*, and the wire 4: to the regmaining terminal of the armature. This dynamic braking circuit willquickly bring the loadto rest which will be prevented from armature A in a-direction opposite to its former direction, the wire 3, the contact 0*, the brush 0, the contact 0 the wire 1 and the brake-winding B, and the field winding F to the negative supply wire 2. .The current in this circuit obviously causes the brake controlled by the winding B to be released and the motor armature to rotate in the opposite direction, thereby causing the load to be lowered; The armature remains connected in a closed circuit with the resistance R The rotation of the armature in lowering causes the arm k to descend, permitting the weight w to rotate the controller Eback to its former position, shown in Fig. 1. The contacts g g first leave thefingers efl-eflthereby opening the said closed circuit around the armature. Immediately thereafter the contact 9 engages the finger e and the contact 9 leaves the finger 6 The circuit is now as follows: from the positive supply wire 5 through the right-hand half of the resistance R, the right-hand section of the contact 0 the brush 0 the contact 0 the wire 7, the finger e, the contacts g, 9*, the finger 6 the wire i, the armature A, the wire 3, the contact 0 the brush c, the first section of the contact 0 the left-hand half of the resistance R 1 the wire 1 and the brake-winding B, and the field-winding F to the negative supply wire 2. The current in this circuit flows in series through the field, the armature, and tie resistance R, the direction of the current through the armature being unchanged. The load may now be lowered under the rheostatic control of the operators controller C in an obvious manner. To stop the motor the handle a is moved to the position shown, whereupon the motor and brake circuits are opened, thereby permitting the brake-Winding to release the brake.

I claim 1. In a motor control system, a motor, a controller for the motor, and a switching device for stopping the motor comprising a means for opening the motor circuit between the motor and the controller, means for closing a circuit from the source through the motor field Winding, and means for closing a local circuit through the motor armature exclusive of the controller.

- In-a motor control system, a motor, a controller for the motor, and a switching device operated by themotor and compris-' .ing means for separately exciting the motor field, and means for shunting the motor armature through a circuit independentof the controller.

3. In a motor control system, a motor having a series field Winding, a controller for the motor, a switching device for separately exciting the series field through a circuit independent of the controller, and connecting the motor armature in a closed cirsuit, and means operated by the motor for operating the switching device.

+i-. in a motor control system, a motor, a 'i and a switching device for stopping the. mo-

orake-Winding, a controller for the motor,-

tor comprising a means for deenergizing the brake-Winding, means for closing a circuit from the source through the motor field Winding independent of the controller, and means for closing a local circuit through the motor armature.

5. In a motor cont 01 system, a motor, a reversing controller rerefor and a device operated by the motor and comprising means for opening-,the motor circuit through the controller, means for closing a shunt around the armature, and means for closing a circuit through the motor field and independent of the controller and for including the armature in the motor circuit when the controller is reversed.

6. In a motor control system, a motor,- controller contacts for connecting the motor armature and field in series to a source of supply, and a switching device operated by the motor for connecting the motor field to a source of supply exclusive of the controller contacts and connecting the motor armature in a closed circuit exclusive of the controller contacts.

Signed at Pittsburgh, Pa, this 8th day of January, 1913.

LESTER C. HART, Vitnesses Arron E. DUFF, F. N. BARBER. 

